1. Field of Invention
The present invention relates to a circuit and a method for providing absolute information for a floating grounded integrated circuit (IC).
2. Description of Related Art
For an IC to operate, it requires a high operation level (often expressed as VDD) and a ground level (often expressed as VSS or GND). In a normal case, the ground level is 0V, a fixed level, such as in the prior art shown in FIG. 1, the ground pin GND is connected to ground (0V). However in certain case, in order to reduce the voltage difference between the high operation level and the ground level such that internal devices of the IC do not require a high specification, a floating grounded IC is proposed. Referring to FIG. 2 which shows an LED (light emitting diode) driver circuit, wherein a power transistor Q, a diode DF and an inductor L forms a buck power conversion circuit; the IC 100 controls the operation of the power transistor Q to convert an input voltage Vin across an input capacitor Cin to an output voltage Vout stored in an output capacitor Cout, and the output voltage Vout is provided to LEDs. A sense resistor Rcs generates a current sense signal which is fed back to the IC for controlling the current through the LEDs. In this prior art, the ground pin VSS is connected to a node PH. When the power transistor Q is turned ON, the voltage at the node PH is equal to the input voltage Vin minus a voltage drop caused by the on-resistance of the power transistor Q and the sense resistor Rcs, and when the power transistor Q is turned ON, the voltage at the node PH is equal to 0V minus the voltage drop caused by the diode DF, so the voltage at the node PH is not at a fixed level, and therefore the ground level VSS of the IC is floating. In the following context of this specification, in order for the terms to express clear meanings, the reference GND is used for indicating an absolute ground level, while the reference VSS is used for indicating a floating ground level (even though VSS is often used for indicating an absolute ground level in the technical field of this invention, this term VSS will be used dedicatedly for indicating a floating ground level in the following context of this specification).
Although the prior art shown in FIG. 2 can reduce the voltage difference between the high operation level and the ground level, it has a problem that the IC is applied to a system which controls the IC by, or transmits to the IC, signals operating with reference to the absolute ground. (In the following context of this specification, such signals which operate with reference to the absolute ground will be referred to as “absolute signals”. Such absolute signals for example may be an analog or digital control signal or a series of control signals, or one or more voltage levels.) The prior art floating grounded IC can not handle these control signal (s) or voltage level (s).
In view of the above, the present invention a circuit and a method for providing absolute information for a floating grounded IC to solve the problem in the prior art, such that a floating grounded IC can recognize information carried by an absolute signal such as control information or a voltage level (referred to hereinafter as “absolute information”), but does not require a complicated circuit or processing steps.